Recently, mobile devices that are driven by a secondary battery or the like and perform radio communication at short ranges using RFID (radio frequency identification) are put into widespread use. Regarding the RFID, see Japanese Laid-Open Patent Publication No. 2009-065426. There is a demand for a small-sized, built-in antenna used in the mobile devices. However, the use of a small-sized antenna may reduce communication performance of the mobile devices due to reduction of the gain. Therefore, some mobile devices in recent years are improved to save the arrangement space of an antenna in the device and maintain the communication performance.
Some improvements for such mobile devices are known: one of the improvements is to stick an antenna formed into a thin film to a battery pack including a secondary battery, and another is to arrange a slim piece of an antenna in a lateral or lower corner portion of a housing of the device. However, in the related art, in many cases, a configuration into which an antenna is formed must be decided based on the free space in the mobile device. In many cases, the configuration and the arrangement location of the antenna must be changed to match the size and the configuration of the mobile device. Hence, there has been a need for taking into consideration the configuration and the arrangement location of an antenna for each of individual mobile devices.
If the arrangement location of an antenna in a mobile device is changed, an impedance of the antenna with the latter-stage circuit in the mobile device is also changed. Hence, according to the related art, matching of the impedance of the antenna must have been performed for each of individual mobile devices, and a process of mounting the antenna in the housing has been complicated.